Field of the Invention
The present invention relates to an image processing device to eliminate noise superimposed on the radiation image and particularly relates to an image processing device so as to improve quality of the image of each frame constituting a live image.
Description of the Related Art
A medical facility equips a radiation imaging device to acquire the radiation image. Some radiographic devices can continuously image the radiation image and then output the results as a video. Such video can be called as a live image (e.g., refer to Patent Document 1.)
Since irradiation of low-dose radiation to the subject is used to provide the live image, the S/N ratio thereof is inferior to the S/N ratio for static imaging (spot imaging) and a lot of noises are included therein. The radiographic device equips an image processing device so as to reduce such noise. Such image processing device can structurally provide the noise reduction image having the S/N ratio improved by superimposing two continuous frames with time.
However, the live image is a video catching the movement of the subject. Accordingly, the image processing by which the two continuous frames are simply superimposed may provide a noise reduction image of which the subject images are as if doubled. Because the incorporated position and shape of the subject are different each other between frames. In addition, since the level of misalignment between the subject's images per se varies depending on the portion of the frame, even if one frame is just shifted relative to another frame to superimpose, doubling of the images cannot be prevented.
Thus, according to the conventional constitution, a structure so as to improve such defect has been adopted. Specifically, the frames are superimposed while confirming conformity of the subject images relative to each portion of the frame. The inventor specifically sets forth the correction method thereof. Here, one frame (first frame) out of two frames is segmented to fine blocks and one of the blocks is noticed. A pattern indicating a part of the subject image is incorporated into the noticed block. This pattern is called as a notice pattern.
Here, another frame (second frame) is considered. The second frame is almost the same image but not exactly the same image as the first frame. Specifically, the notice pattern relative to the first frame has moved to somewhere on the image with regard to the second frame. Conversely, the area incorporating the notice pattern on the first frame must be somewhere on the second frame. Such area has the same shape and size as the notice block of the first frame but the occupying position on the frame is not guaranteed to be always the same between frames.
According to the conventional image processing device, the area incorporating the same pattern as the notice pattern on the notice block of the first frame is searched out from the second frame and then those patterns are superimposed each other and the superimposition processing relative to the notice block is accomplished. The image processing device executes the same superimposition processing relative to all blocks on the first frame and generates one noise reduction image by connecting the superimposition results acquired at this time (e.g., refer to Patent Document 2.)